GUANINE-NUCLEOTIDE-BINDING PROTEINS MEDIATE THE CHEMOTACTIC SIGNAL OFTRANSFORMING GROWTH-FACTOR-BETA-1 IN RAT IL-2 ACTIVATED NATURAL-KILLER-CELLS

Transforming growth factor (TGF)-beta1 induced rat IL-2-activated natu ral killer (IANK) cell chemotaxis. Various doses of cholera toxin (CT) or pertussis toxin (PT) inhibited the activity of TGF-beta1 suggestin g a role for guanine nucleotide binding (G) proteins. ADP-ribosylation assay showed that rat IANK cell membranes possess a 39 kDa PT substra te and two, 41 and 42 kDa, CT substrates. ADP-ribosylation also showed that incubating IANK cell membranes with TGF-beta1 in the presence of guanosine 5'-O-(3-thiotriphosphate) resulted in the disappearance of the PT substrate. Immunoblot analysis showed that rat IANK cell membra nes possess one G(i) (39 kDa), one G0 (39 kDa) and three G(s) (40, 41, and 42 kDa) proteins. Pretreatment of IANK cell membranes with TGF-be ta1 in the presence of guanosine-5'-O-(3-thiotriphosphate) reduced the intensity of the 39 kDa G0 and the 40 kDa G(s) but not the 39 kDa G(i ) or the 41 kDa or 42 kDa G(s). Furthermore, TGF-beta1 stimulated GTP binding and increased GTPase activity in IANK cell membranes. Both act ivities were inhibited by PT or CT. This inhibition was associated wit h the modification of G proteins by the toxins suggesting that bacteri al toxin substrates are linked to TGF-beta1 receptors. Our results sug gest that G0 and G(s) are involved in mediating the chemotactic signal of TGF-beta1 in rat IANK cells.